Process for reduction of core losses in cube textured iron-silicon alloys



United States Patent 3,513,039 PROCESS FOR REDUCTION OF CORE LOSSES IN CUBE TEXTURED IRON-SILICON ALLOYS Dietrich Ganz, Hanan, Germany, assignor to Vacuumschmelze G.m.b.H., Hanan, Germany, a corporation of Germany N0 Drawing. Filed May 12, 1967, Ser. No. 637,914

Claims priority, application Germany, Sept. 14, 1966, 31 9 v 35 Int. Cl. 021d 1/26', 7/02;Htl1f 1/04 US. Cl. 148-111 9 Claims ABSTRACT OF THE DISCLOSURE This application is based upon my German application V31,935 VIa/18c, filed Sept. 14, 1966.

BACKGROUND OF THE INVENTION Cube textured or double oriented iron-silicon sheet alloy is designated as having, in Miller 'Indices, the major proportion of volume of its grains in the (100) [001] orientation. In an alloy sheet having this grain texture the crystal lattice of a typical grain may be visualized as a cube having two faces thereof lying in planes parallel to the sheet plane and four planes thereof perpendicular thereto, and four cube edges aligned in a direction parallel to the rolling direction while four other cube edges are aligned in a direction perpendicular to the rolling direction and transverse of the sheet. In a sheet having a cube grain texture of this type the easiest directions of magnetization are in the rolling direction and perpendicular thereto.

Cube textured iron-silicon alloy sheet material has undergone substantial development and is to some extent in commercial use. One process for making such material is set forth in US. Pat. No. 3,240,638, dated Mar. 15, 1966, by G. W. Wiener et al. It is desirable that the great majority and preferably at least 70% of the volume of the sheet comprise cube textured grains, that is (100) [001] orientation, with the cube faces of such grains being parallel to the sheet surface within approximately and the cube edges being within of the direction of rolling.

Cube-textured iron silicon sheet material of the type described, in which a preferred magnetic direction lies in the plane of the sheet in both the rolling and transverse directions, is employed in the manufacture of magnet cores for communications equipment, for special transformers for motors and generators and for magnetic amplifiers. The full utilization of this double oriented iron-silicon alloy material requires particularly, in the manufacture of magnet cores made from punched laminations, that the total losses occurring in the magnet'ones be held to as low a level as possible.

The total losses in cores of concern in this invention, may be said to be made up principally of hysteresis and eddy current losses. The hysteresis loss is directly proportional to the area of the hysteresis loop and is also directly proportional to frequency. The heat losses engendered by induced circulating currents throughout the volume of the core are referred to as eddy current losses. The total eddy current loss is proportional to the square of the frequency.

There has been little or no investigation directed to 3,513,039 Patented May 19, 1970 the problem of reducing the total losses in finished cube textured iron-silicon alloy sheet where the sheet material is to be employed at frequencies just above 50 c.p.s. and higher.

SUMMARY OF THE INVENTION In accordance with the present invention, the eddy current losses in iron-silicon alloy sheet containing from 2 to 4% silicon with the [001] grain texture are substantially reduced by cold rolling the oriented alloy sheet to effect about 0.5 to 2% reduction in thickness, and finally annealing the alloy sheet in a protective atmosphere at a temperature of from 750 to 1100 C. The decrease in total losses becomes significant at frequencies somewhat above 50 c.p.s.

It has been found in the past that any general cold working'of an alloy sheet material having cube grain texture leads to large increases in hysteresis losses as determined from observing that this increases the static hysteresis loop. These substantial increases in hysteresis losses due to substantial cold working cannot be completely eradicated by subsequent annealing, and consequently, an increase in total losses is the final result of such cold working.

It has also been observed that the total losses in ironsilicon alloy sheets cold worked a substantial amount are increased when alternating fields having frequencies of, for example, 50, 400 and 1000 cycles are applied.

It has been found that, contrary to such earlier experience, a substantial reduction in losses in the ironsilicon alloy sheet materials With which this invention is concerned is accomplished in a preferred manner when the magnetic sheets are cold rolled effect to about a 0.5% to 2% reduction in thickness and optimum results are obtained when the cold reduction is from 0.5% to 1.2%. A temperature of about 800 C. has proved to be particularly suitable for carrying out the subsequent annealing process. Dry hydrogen, having a dew point of 40 C. or lower is suitable for use as the protective atmosphere during the annealing process. Other suitable protective atmospheres are argon, helium and a vacuum of the order of 1 micron. The period of annealing can range from about one-half to four hours.

The object of the invention is the provision of process whereby the alternating current losses in a cube grain texture iron-silicon alloy may be substantially reduced.

Other objects of the invention will, in part, be ob vious, and will, in part, appear hereinafter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples are presented to illustrate the process of the invention.

Example I A strip of sheet material consisting of an iron-silicon alloy with a silicon content of 3%, by weight, and a thickness of 0.2 mm. (8 mils), which has over 70% by volume of (100) [001] grain texture, is subjected to a reduction in thickness of 1.7% by cold rolling and is thereafter finally annealed for a period of one and onehalf hours at a temperature of 800 C. in dry hydrogen having a dew point of 45 C. The losses measured on the metal strip before and after treatment in accordance with the invention as described above, are set forth in the table following Example II.

Example II A strip of sheet material consisting of an iron-silicon alloy with a silicon content of 3% and a thickness of 0.1 mm. (4 mils), and which has over 70% by volume of (100) [001] grain orientation, is subjected to a reduction TABLE 2. A method in accordance with claim 1, in which the 'cold Working consists of cold rolling the sheets to a reduction in thickness of from about 0.5 to 2%.

3. A method in accordance with claim 1, in which the cold working consists of cold rolling the sheets to a reduction in thickness of from 0.5 to 1.2%.

Losses per cycle in rnwsecJkg.

Hm w 50 P lflo E ili Pm 1900 E 1on0 Example I: 0.2 mm. sheet (a) 2. 3 12. 8 10. 5 33. 8 31. 5 51. 5 49. 2 Cold-rolled 1.7%+1.5 hr. at 800 C Hz Example II: 0.1 mm. sheet (a) 3. 3 10. 0 6. 7 26. 3 23 87. 6 34. 3 Cold-rolled 1.2%-+1.5 hm at 800 C., H

The symbols in the table have the following meaning: (a) =Initial condition. (b) Final condition after cold rolling and annealing. Hro=Losses at an induction of 10 kg. in a steady field (pure hysteresis losses). P10 Losses at an induction of 10 kg. and a 50 cycle alternating field. Pm =Losses at an induction of 10 kg. and a 100 cycle alternating field. P1 Losses at an induction of 10 kg. and a 1,000 cycle alternating field. Ew =Eddy current losses=Pr H10. E =Eddy current losses=P Hm. E1o =Eddy current losses=P H u.

It will be observed from the above table that a reduction in the total losses, P, at frequencies above 50 cycles occurred when cube texture sheets were given a cold reduction in the range of about /2% to 2% followed by an anneal at a temperature of 750 to 1100 C. in a protective atmosphere.

Further, from the above table, it is seen that at 50 cycles per second the total losses of untreated and treated sheet material are substantially equal. At 400 c.p.s. and 1000 c.p.s. the losses of the treated sheet material are substantially lower than the untreated sheet material.

The effect of the treatment of the invention on eddy current losses is strikingly illustrated in the table. The eddy current losses (E) are calculated for each frequency by subtracting from the total losses (P) at the stated frequency, the pure hysteresis losses (H). The table shows improvements in eddy current losses at all frequencies tested for the treated sheet. In the case of the 0.1 mm. sheet which was cold rolled 1.2% a decrease in eddy current losses of at least about 30% was accomplished at the tested frequencies.

It is believed that the losses due to hysteresis have increased as a result of the cold working and annealing of the original sheet material, but that the losses caused by eddy currents have decreased to a much larger extent and, as a result, an overall reduction is obtained in the total losses.

While the phenomena associated with the decrease of losses in cube texture grains of iron-silicon alloys have been explained as they are presently understood, the applicant does not wish to be bound by any particular theory,

since regardless of theory, the method of my invention will successfully reduce the losses of cube texture ironsilicon alloys.

It will be understood that the above description and drawings are illustrative and not limiting of the invention.

I claim as my invention:

1. A method for reducing eddy current losses in ironsilicon alloys having a (100) [001] grain orientation, comprising essentially the steps of lightly cold working an alloy member having at least 70% by volume of the grains displaying a (100) [001] crystallographic orientation with the cube faces being within about 5 of the member surface and the cube edges being within in the plane of the member in the direction of Working and in the transverse direction, said cold working effecting a reduction in thickness not in excess of about 2% and thereafter annealing the member in a protective atmosphere.

4. A method in accordance with claim 2, in which the annealing is carried out at a temperature in the range from 750 to 1100 C.

5. The method of claim 4 in which the protective atmosphere is dry hydrogen.

6. A method in accordance with claim 4, in which the annealing is carried out in a protective atmosphere of dry hydrogen having a dew point of about 40 C. and lower.

7. The method of claim 6 in which the annealing is carried out for a period of from one-half to four hours.

8. The method of claim 2 in which the annealing is carried out at a temperature of about 800 C. for a period of one-half to four hours.

9. A method for reducing total losses at frequencies about 50 c.p.s. in iron-silicon alloys having a (100) [001] grain orientation, comprising essentially the steps of cold rolling an alloy member having at least by volume of the grains displaying a [001] crystallographic orientation with the cube faces being within about 5 of the member surface and the cube edges being within 15 in the plane of the member in the direction of Working and in the transverse direction to the Working direction, said cold rolling effecting a reduction in thickness of from 0.5% to 2% and thereafter annealing the member in dry hydrogen having a dew point of about 40 C. for a period of from onehalf to four hours at a temperature of from 750 to 1100 C.

References Cited UNITED STATES PATENTS 1,867,818 7/1932 Freeland 148-111 2,067,036 1/1937 Wimmer 148--1 11 2,535,420 12/1950 Jackson 148-111 2,738,295 3/ 1956 McKnight et al 148113 3,212,942 10/1965 Takahashi 1481 12 3,240,638 3/1966 Wiener et al 148111 X 3,415,696 12/1968 Gimigliano 148l12 X FOREIGN PATENTS 464,450 4/ 1950 Canada.

L. DEWAYNE RUTLEDGE, Primary Examiner G. K. WHITE, Assistant Examiner US. Cl. X.R. 148--ll2, 113 

